In recent years, low-CO2 emission, fuel-efficient hybrid cars (HEVs; Hybrid Electric Vehicles) have been increasingly common. Such a hybrid car is mounted with a motor as a power source other than an engine, and a secondary battery for supplying electric power to the motor. The vehicle-mounted secondary battery typically employs a lithium ion battery or nickel hydride battery. In order to control energy balance of the vehicle-mounted secondary battery, changing a current rate for each state of charge (SOC) range of the secondary battery is known (for example, refer to Patent Literature 1).